That shows that they apparently do not all age at the same rates. Almost a random thing.
Not random at all as the life of a tube is affected by usage (on / off cycling), circuit design, and the load it works with.
The next time you have your hands on an all-glass Five Tube All America take a peek through the back cover as you turn it on. Not unusual for one of the tubes to light up faster & hotter, then drop to a lesser glow as the other tubes come up to temperature. That tube will be more prone to a blown heater than the rest but it is possible another tube will go weak (low emissions) before that happens. Change the weak tube and the dynamics of the filament string could change enough to delay the filament failure even further. In a transformer operated radio the tubes most likely to fail usually run the hottest. Rectifier and audio output typically, but low power IF amplifiers like a 6AU6 tend to last almost forever. I have never found a bad 6H6 or 6AL5. That's a dual diode detector (same tube with the 6H6 an 8-pin Octal and the 6AL5 a 7 pin Novar) and operate under almost no load or power dissipation. Which makes a huge difference as they run very cool and have small heaters.
In TV's from the day the tube most likely to fail was the horizontal output. Usually the largest and hottest tube in the set except for the CRT (largest) which tended to be the last tube to fail... And that's a bit of a play on words because a CRT replacement was expensive enough that junking the set usually made more sense. So when the CRT failed that would tend to be " the-last-tube-to-fail ". Why replace the highest dollar part in a set with 10 years on the clock when a new TV with all-new parts and warranty was within a hundred bucks or so?
Which explains why you're more likely to find a Fabulous 50's radio than a TV from the same era.............. The radio could be kept in repair far longer and for less money than the TV.
BTW: Here's a related trivia item: What was the best selling American car in 1957? It was the Ford Fairlane. Which is the most restored car from 1957 and probably the most collected car of all time? That's the 1957 Chevrolet Belair.